1. Field of the Invention
This invention relates to an image forming apparatus, such as an electrophotographic copier, an electrophotographic printer or the like, and more particularly, to an image forming apparatus including a device for cleaning a charging means thereof.
2. Description of the Related Art
In an electrophotographic image forming apparatus, toner, dust or other contaminant particles are often airborne inside the apparatus. When copying operations are repeated for a long time period, these contaminant particles adhere to the shielding electrodes, and the corona wire (charging wire) electrodes of a corona charger incorporated in the apparatus. The contaminant particles accumulate in the respective units of the charger in accordance with an increasing number of copying operations. After about a few thousand copying operations, a decrease in charging efficiency, and uneven charging and charge-removing begin to occur due to the above-described adhering of contaminant particles. Consequently, the quality of copied images decreases.
In a conventional approach to overcome the above-described problems, for example, the user or serviceman of the copier periodically takes out the charger from within the apparatus to clean the charger, or cleans the charger accommodated within the apparatus by inserting a cleaning tool into the apparatus. However, a corona wire is in general a conductive thin wire made of tungsten or the like, and is apt to be cut by even a slight error in the cleaning operation. In addition, it is difficult to prevent a decrease in picture quality because the user may forget to periodically clean the wires. Further, it is necessary to clean contamination inside the charger after taking out the charger and visually confirming the contamination, and such an operation is very troublesome. Actually, the user often notices contamination inside the charger only after finding a decrease in the quality of copied images, and thereafter cleans the charger. Hence, it is difficult to always maintain the charger in a satisfactory state.
In order to overcome such problems, there have been proposals in which a charger is provided with a corona wire cleaning member movable along the corona wires, and a driving mechanism for moving the cleaning member. The corona wires are automatically cleaned by appropriately operating the driving mechanism in accordance with a program preset in a control circuit without taking out the charger from within the main body of the apparatus. Alternatively, a cleaning operation is occasionally performed by inputting an operational signal to the driving mechanism using a manual switch whenever necessary (see, for example, U.S. Pat. Nos. 3,842,273, 3,870,833 and 3,965,499, and Japanese Patent Application Public Disclosures (Kokai) Nos. 54-28633 (1979) and 62-288865 (1987).).
Since the charger is a consumable unit, it is provided as a service unit detachable from the apparatus. In an automatic cleaning means of a conventional charger, it is considered to be advantageous from a viewpoint of cost to provide only the cleaning means in the charger, and to provide a driving means in the main body of the apparatus.
Accordingly, it is necessary to have a configuration in which the cleaning means engages the driving means in order to form a transmission channel to transmit the driving force of the driving means to the cleaning means. Also it is necessary to have the cleaning means re-engage the driving means when the charger is mounted on the apparatus after first detaching the charger from the apparatus.
In a conventional configuration, the driving means engages the cleaning means by utilizing a difference between the upward and downward movements of the charger produced when the charger is in an operational state and in a non-operational state.
Such a configuration can be applied to a charger having upward and downward movements used, for example, in transfer and separation, but cannot be applied to a fixed charger used, for example, as a primary charger, or a post charger provided between development and transfer operations.
In addition, if the engagement between the cleaning means and the driving means is not securely performed, only the driving means freely reciprocates while the cleaning means does not move. Hence, the charging wires are not cleaned at all.